Abstract
The extracellular matrix of plants, algae, bacteria, fungi, and some archaea consist of a semipermeable composite containing polysaccharides. Many of these polysaccharides are O-acetylated imparting important physiochemical properties to the polymers. The position and degree of O-acetylation is genetically determined and varies between organisms, cell types, and developmental stages. Despite the importance of wall polysaccharide O-acetylation, only recently progress has been made to elucidate the molecular mechanism of O-acetylation. In plants, three protein families are involved in the transfer of the acetyl substituents to the various polysaccharides. In other organisms, this mechanism seems to be conserved, although the number of required components varies. In this review, we provide an update on the latest advances on plant polysaccharide O-acetylation and related information from other wall polysaccharide O-acetylating organisms such as bacteria and fungi. The biotechnological impact of understanding wall polysaccharide O-acetylation ranges from the design of novel drugs against human pathogenic bacteria to the development of improved lignocellulosic feedstocks for biofuel production.
Highlights
We provide an update on the latest advances on plant polysaccharide O-acetylation and related information from other wall polysaccharide O-acetylating organisms such as bacteria and fungi
A sequence comparison of nine representative embryophytic species showed that ALTERED XYLOGLUCAN 9 (AXY9), TBL29, and RWA2 proteins seems to be highly conserved in dicots (Arabidopsis thaliana and Populus trichocarpa), monocots (Oryza sativa) and gymnosperms (Pinus radiata) sharing identities higher than 50% and similarities around 75% with the Arabidopsis representatives
Since algal REDUCED WALL O-ACETYLATION (RWA) orthologs do not contain a GxxH and/or GSD domain required for polysaccharide O-acetylation algae might harbor additional, hitherto unidentified proteins that would be necessary for O-acetylation to occur. These results indicate that RWA proteins emerged earlier than AXY9 and the TBLs and suggest that green algae may use a polysaccharide O-acetylation system based on RWA
Summary
A second periplasmic protein with demonstrated acetylesterase activity -PatB2- has been involved in O-acetylation of additional cell wall components the exact donor/acceptor substrate remains to be discovered (Sychantha et al, 2017) These organisms seem to have developed two different, independent systems for the translocation of acetyl-groups to O-acetylate the various wall polysaccharides utilizing members of two or more O-acetyl transferase families. Gram-positive bacteria, fungi, and mammals developed a one component machinery to O-acetylate extracellular polymers These systems use a single protein combining a multiple transmembrane domain translocating acetyl groups from the cytoplasm fused to a globular domain, containing a SGNH/GDSL-like catalytic motif. Plant RWA proteins belong to the same sugar acyltransferase superfamily containing 10 transmembrane domains as bacterial OatAs, CnCas1p, and HsCasD1, they lack the globular O-acetyltransferase domain, indicating that plants need the additional involvement of other components such as members of the TBL family and/or AXY9 in order to O-acetylate their wall polysaccharides.
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